Integration of Diagnostic and Interventional MRI for the Study of Persistent Prostate Cancer after External Beam Radiotherapy

Purpose: To adapt a magnetization-prepared RF cycled spiral imaging technique, termed T1prep, for time-efficient RF-insensitive clinical prostate T1 quantification at 1.5 tesla, and evaluate SNR limits to voxel-based T1 mapping. Materials and Methods: A magnetization-prepared spiral imaging technique was adapted for robust T1 contrast development, multi-slice imaging within 5-minutes, and data regression to a monoexponential decay. In vitro testing evaluated RF insensitivity of the multi-slice acquisition plus method accuracy. A clinical pilot study was performed in fifteen patients with low or intermediate risk localized prostate cancer. Results: The multi-slice design displayed excellent RF insensitivity (<1% error for RF mistunings to ±20%), and accuracy (within 0.5% of gold standard for T1 values within 1500 ms). A clinical pilot study reported equivalence between central gland (CG) and peripheral zone (PZ) T1 values (CG: 1321±45 ms, n=14; PZ: 1359±204 ms, n=11) and reduced tumor T1 (1196±106 ms, p=0.028 and 0.048 compared to CG and PZ). SNR measurements identified an inappropriateness of voxel-based analysis. Conclusions: T1prep can quantify prostate T1, as an adjunct measure for quantitative perfusion measurements in radiotherapy trials. Intra-patient heterogeneities support T1 assessment within individual patients. SNR calculations will guide protocol improvements towards voxel-based analysis in future trials.